1. Field of the Invention
The present invention relates to an improved image reading apparatus for optically reading the contents of a document being conveyed to obtain corresponding image information.
2. Description of the Related Art
As is well known in the art, a facsimile apparatus comprises a reading device for optically reading an image on a sheet-like document, such as a letter, a picture, a photo, and the like; a conveying mechanism for conveying the document to the reading device; a coding device for converting the image data which has been read by the reading means as an electric signal into digital data and coding it; a transmitter for transmitting the coded data to a transmission path; a receiver for receiving data coming from the transmission path; a decoder for decoding the data which has been received by the receiver into original image data; and a recording device for recording the decoded image data on a recording paper.
When a transmitting-side facsimile apparatus is linked to a receiving-side facsimile apparatus via a transmission path, such as a telephone line, with a document set on the transmitting-side facsimile apparatus, the transmitting-side facsimile apparatus is operated so that the reading device reads out an image on the document being conveyed, the coder encodes digital data to which the read-out data has been converted, and the transmitter transmits the encoded digital data as a modulated signal via the transmission path. In the receiving-side facsimile apparatus, on the other hand, the receiver receives a signal being transmitted over the transmission path, the decoder decodes the coded data which has been modulated back to original image data, and the recorder receives the image data, and records it, as a reproduced image on a recording paper sheet.
Such conventional facsimile apparatus can treat any document as transmitted image data and transmit any imageable information, such as a printed character and a picture, a photo, a hand-written character and a picture, or the like.
A general arrangement of a conventional facsimile apparatus will be explained below with reference to FIG. 12.
As shown in FIG. 12, a housing 1 for a facsimile apparatus has a document insertion inlet 1a for setting a document on a proper location, a document delivery outlet 1b and a recording sheet outlet 1c. A document rest 10 is provided relative to the document insertion inlet 1a to allow the document whose image is to be transmitted to be held in place at a slanted angle. The document is set on the document rest 10 with its forward end slantwise placed in contact with a guide 9a in the housing 1. The guide 9a is located opposite to a guide 9b so that the document can be guided over a feed roller 3 past a location between these guides. The feed roller 3 is located below and in contact with the guide 9a.
Upon setting a plurality of sheet-like documents on the document rest 10, superimposed documents have their forward ends obliquely rearranged so that the bottommost document first reaches a nip between the feed roller 3 and the guide 9a. Since only the bottommost document directly contacts with the feed roller 3, the bottom most document is fed downstream of a delivery path with the rotation of the feed roller 3.
A pair of feed rollers 4a, 4b are situated downstream of the feed roller 3, followed by a roller 5 and an imager system 8. Of these rollers, the rollers 4a and 4b are a drive roller and pinch roller, respectively. The rotational speed of the roller 4a is set to be faster than that of the roller 3 and thus a preceding document is fed faster than a following document. As a result, even if a plurality of documents are set, on over another, one the document rest 10, they are fed at proper intervals to the imager system 8 in a sheet-by-sheet fashion. The roller 5 is so arranged as to be in contact with the surface of the imager system 8. The roller 5 is rotated at the same rate as the second feed roller 4a so that the feeding document is fed toward the downstream side while being in firm contact with the imager system 8. Downstream of the imager system 8 are provided a pair of rollers 6a, 6b through which the document which has been read out by the imager system 8 passes. The document then is discharged toward the document delivery outlet 1b. A sensor 7 is located near the document insertion inlet 1a in the housing 1 to detect the presence of a document DP. When the document DP is detected by the sensor 7, then the facsimile apparatus enters a stand-by state is started. The aforementioned arrangement is generally required to read out the document so that image data may be obtained.
The facsimile apparatus includes a printing unit 12 for recording the image data on a recording paper sheet, a roller 11 for discharging the recording sheet 13 toward the corresponding delivery outlet 1c, and so on. Also required are a circuit unit for control, a control unit for communication and transmission, a display, various types of keys, various types of indicator lamps, etc., but they are omitted for the sake of brevity.
FIGS. 13 and 14 are a front view and side view, respectively, showing an image reading apparatus for document readout on the facsimile apparatus.
The image reading apparatus as shown in FIGS. 13 and 14 is composed of the roller 5 and imager system 8 of FIG. 12. Stated in more detail, as shown in FIGS. 13 and 14, a pair of paper guides 101 and 102 for document guide are arranged in a vertical positional relation with an elongated slit 103 formed in the lower paper guide 102 in a direction perpendicular to that in which the document is conveyed.
A transparent plate-like stage 104, such as a glass plate, is located in the slit 103. A light source 105, a lens 106 and a light-receiving sensor 107 are provided below the paper guide 102, and the roller 5 is disposed above the stage 104. The roller 5 is located along a direction perpendicular to that in which the document is conveyed and has a length large enough to cover the width of a document of a largest size handled on the facsimile apparatus. The roller 5 is located in contact with the stage 104 and rotatably supported by a pair of roller support members 109a, 109b at both the ends. The roller support members 109a and 109b are mounted, for example, on a paper guide 102.
The roller 5 is made of, for example, a white-color rubber or resin and used for a reference white-color level. The roller 5 is rotated by a motor, not shown, and can be utilized as a roller for conveying a document as already set out above.
As shown in FIG. 14, the document DP is fed into a site between the paper guides 101 and 102 in a direction as indicated by an arrow in FIG. 14 so as to read out the document image on the reading apparatus. Since the roller 5 is rotated in a direction as indicated in FIG. 14, the document DP is fed past a site between the stage 104 and the roller 5, during which the document DP is conveyed along the stage 104 while being pressed by the roller 5, against the stage 104. A light beam coming from a light source 105 illuminates the document DP through the stage 104 and the reflected beam is imaged at a light-receiving sensor 107 via a lens 106. Thus, the information of the document DP is detected by the sensor 107 as an amount of light reflected and converted to an image signal (an analog signal). In this way, it is possible to read out the information from the document DP.
The imager system 8 uses, as an imaging sensor, a line type light-receiving sensor composed of a CCD (charge coupled device), the arrangement of which is as shown in FIGS. 15 and 16. FIG. 15 is a side view in cross-section showing a pole-like light source 81, a rod lens 84 and at least one light-receiving sensor 86 in a housing 85. The light source 81, rod lens 84, and sensor 86 correspond to the light source 105, lens 106 and sensor 107, respectively, of FIG. 13. A window 83 is provided in the housing 85 and the rod lens 84 and light source 81 are located in the housing 85 such that they face the window 83. A light beam coming from the light source 105 is directed to a roller 5 side through the window 83. A light beam which is reflected from a document being moved beneath the roller 5 is imaged at the light-receiving sensor 86 by the rod lens 84. The sensor 86 is composed of a line-type CCD with a plurality of very tiny light-receiving cells densely arranged, as arrays, in a direction in which the rod lens 84 is situated. An electric signal corresponding to an amount of light detected at the cell array is taken out through a connector 89.
The stage 104, though not shown in FIG. 15, is provided at the location of the window 83.
The light-receiving sensor 86 is composed of arrays 91, 92, 93, 94, . . . , constituted by approximately a few tens to a few hundred of light-receiving cells as shown in FIG. 16. As will be readily understood from the above, image data at each position on the same line of a document can be obtained by controlling the detection timing, etc., of a light-receiving signal which is obtained from the corresponding array so as to handle a displacement from array to array.
In the facsimile apparatus, the roller 5 is white in color and, as shown in FIG. 14, the reference white level of the document DP is set by reading out the white-color surface of the roller 5 by the sensor 86 before the document DP reaches a read position. The imager system 8 utilizes the line-type light-receiving sensor 86 where a plurality of very tiny light-receiving cells are densely arranged in a linear fashion to obtain a space-division resolution.
Since the cells are formed as a semiconductor device, each cell varies in its output characteristic against its input and in its characteristic against a temperature variation and against a variation with time. In order to obtain the accuracy of imaging data output from the respective cells, it is necessary to correct the output level of the respective cells in accordance with a constantly varying output characteristic of the cell.
For such a level correction, it is necessary to know a reference white level.
In order to gain the white-level data, the white-color roller 5 is employed in the image reading apparatus for the facsimile apparatus. A light beam which is reflected on the white-color roller 5 is detected by the respective cells of the imager system 8. The signal level thus detected is utilized as a reference white-color level upon the reading of the document image. Further, the roller 5 of the image reading apparatus is employed as a roller for feeding the document and rolled in contact with the stage 104 or the document DP at all times during use, so that the contact surface of the roller 5, that is, the entire periphery of the roller 5 is liable to be soiled.
Since the signal level that is obtained from the roller surface is utilized as the reference white-color level, if a signal level reflected from a soiled roller is used, it contains a broader soil area a or a local soil area b, as shown in FIG. 17, thus making it difficult to obtain a stable white-color reference signal.
In the conventional image reading apparatus, the reference white-color level of the document is obtained by using the light beam which is reflected from the white-color roller 5 for document feed and for ensuring firm contact of the document with the stage 104. As the roller 5 contacts with the stage 104 or the document DP over its whole surface during feeding of the document, the roller surface is liable to be soiled, thus causing the reference white-color level to become unstable. In order to avoid this problem, frequent cleaning of the roller 5 and frequent cumbersome servicing are necessary.